Method for producing bonded fibrous products



March 7,1967 D..E. W IEGAND ETAL 3,303,213

' METHOD FOR PRODUCING BONDED FIBROUS PRODUCTS Fnedua 24. 19 61 vas .30 22 72 x 70.

Inventors John E. Cadoiie United States Patent 3,308,218 METHOD FOR PRODUCING BONDED FIBROUS PRODUCTS Donald E. Wiegand and John E. Cadotte, Cloquet, Minn.,

assignors to Wood Conversion Company, St. Paul,

Minn., a corporation of Delaware Filed May 24, 1961, Ser. N 0. 112,225 7 Claims. (Cl. 264-121) The present invention relates generally to bonded airlaid fibrous products such as particle board and felted products as flexible blankets, insulation board and hard board. In particular, it relates to the formation of a felted product with improved felting, strength and uniformity.

It is well-known to suspend material containing feltable fibers and/or wood particles in air for deposition, either by gravity or by forced felting, with the objective of intermeshing the depositing particles on and into a mass which is growing in the process of formation, which mass is hereinafter referred to as a mat. Such mats have a relatively low density when formed by gravity fall, and a relatively higher density as the impact of depositing particles is increased, as by differential pressure, for example, by suction under a screen on which the mat is formed, or by discharge from a region of superatmospheric pressure, or both.

Material so deposited my be accompanied in the suspension by binder to deposit with the material, or binder may be applied to the mat face as it is formed. The binder may be a powder, such as thermosetting resin, or a liquid, such as a starch sol or a solution or suspension of thermoplastic or thermosetting binder material. Liquid materials so applied render the particles heavier and this leads to more dense mats. Some liquid binders so used function to lubricate the particles thus to increase the degree of intermeshing on deposition and further lead to more dense mats.

It is the general object of the present invention to limit the degree of intermeshing of depositing particles in such air-laying process, and thereafter, to effect interfelting or intermeshing by mechanical compression of the mat so formed.

It is a particular object of the invention to form a mat by depositing material containing mat-forming particles which carry on their surfaces a tackifying quantity of means to render those surfaces tacky, to compress the mat to a consolidated product in the presence of other means as binder for bonding the particles, and to set the binder.

The word tack is used herein to refer to the material which is added to produce the desired tackiness.

As a result of the invention, the tack-presenting particles fall on a growing mat which also is tacky and tend more to pile than to intermesh. Because the material at the face of the mat is tacky and the contacting material includes the tacky particles, there is resistance to a falling particle penetrating an opening in the mat, and hence, intermeshing is greatly minimized. This is evidenced by the density of a deposited mat. By adding tack to fibers or wood chips or flakes before depositing them, the density of the mat is much lower and the mat much thicker, than when the tacky agent is absent, the conditions otherwise being the same. The lower the density of a mat, the more uniform in density are the products formed by consolidation. In compressing a fiber mat, for example, to interfelt its content, the lower the initial density, the more room there is laterally for individual elements to move in response to compressive force, thereby effecting greater uniformity in density.

In practicing the present invention, the material to be deposited is such that it contains intermeshable particles and in the preferred embodiments, the intermeshable particles predominate in feltable fibers.

The term feltable fibers as used herein contemplates fibers which are capable of randomly felting when deposed from suspension in air to form a mat, thus having the feltable characteristics of individualized vegetable fibers and opened-up bundles thereof, staple cotton fibers, and mineral wool fibers. Asbestos-type fibers occur in nature in great length, but in commerce are of variable lengths, and most commonly in commerce of lengths characterizing them as feltable fibers.

The term feltable particles as used herein means rela, tively small pieces, usually of wood, which may be airlaid to a growing mat of randomly positioned particles and which in so depositing inter-engage or felt in a manner distinguishable from simple piling.

Wood is a common source of such particles and feltable fibers. In converting wood to forms for assembly and consolidation to form fibrous products, the resulting forms are chips, wafers, sticks, opened-up bundles and individualized fibers. All such forms can be intermeshed or felted, using that term in a broad sense. Opened-up bundles of fibers present fiber ends and interstices which participate in fiber felting. In producing feltable fibers from wood, a common method is to reduce wood chips by rubbing processes, for example, that of the US. Asplund patent, US. No. 2,008,892, of which the apparatus can be adjusted to produce a variety of mixtures of individualized fibers, opened-up bundles of fibers and so-called matchsticks. Such mixtures are the preferred material for use in the present invention. Where more refined and less woody felts are desired, chemically digested wood may be used, such as semi-chemical pulp, or cellulose pulp. As an example of cellulose pulp, the grade thereof known as sulfite screenings is useful, these containing some portions of the digested wood not fully reduced to individualized fibers, but chemically relieved of much of its natural lignin.

In practicing the present invention, various air-laying processes may be used, such as the gravity deposition processes may be used, such as the gravity deposition processes represented by US. Patents Nos. 2,363,480, 2,493,194, 2,544,019, 2,624,079 and 2,646,381, some being operable with or without suction, and differential pressure processes represented by US. Heritage Patent No. 2,757,150. For the best results as measured by the lower density of deposited mats, gravity deposition is preferred. But, the capacity or rate of production may be increased when differential pressure methods are used.

Since the invention contemplates depositing intermeshable or feltable particles with tack thereon, and since the depositing material containing the particles must be dispersed in air for deposition, it is necessary to apply tack at some stage prior to deposition. For many reasons, it is most practicable to disperse the material in air and during its passage through air for deposition, to apply tack-producing means to the dispersed material. The preferred method is to spray tack-producing material in a liquid form into air-dispersions of the particles. The liquid form may be a melted tack substance such as asphalt or pitch, but more conveniently it is a solution or dispersion of the tackifying means, in a volatile liquid vehicle, preferably water.

In using such an aqueous dispersion, the degree of tack is influenced by the proportions of tack means and of water including the water or moisture content of depositing material itself, for example, the moisture content of fiber. The total amount of water present at the time of contact is a factor subject to control to effect the desired degree of tack.

However, the preferred method for ease of control of water content is to apply an aqueous liquid containing both the tack-producing means and the binder means.

Among the materials available for tackifying and those for bonding, numerous ones have both tackifying capacity and bonding capacity. Many are better in one respect than in the other, making it important to select one agent for tack and a second agent for binder with the understanding that each to a degree may enhance the function of the other. In general, it has been found that the tackifying agents used to supply tack, give poor strength if depended upon for all the bond. Therefore, a bonding agent is used in addition, and it is chosen for the strength or other properties desired.

Among the tack-producing means which may be used are certain lignin compounds from wood or bark, resinous residues from distilling pine extract, certain carbohydrates, such as dextrins, corn syrup, and converted starches, protein glues and the like. Suitable water-soluble lignin compounds are salts of lignin sulfonic acid with sodium, potassium, ammonium, calcium or magnesium. Other lignin compounds are mentioned later. A pine residue known as Vinsol, sold by Hercules Powder Company, Wilmington, Delaware, is water-insoluble, but when melted and then emulsified in water, it may be used to provide tack. Vinsol is the residue after distilling terpertine and rosin from an extract of pine wood by a hydrocarbon solvent such as gasoline.

Among the binder means which may be used are activatable comminuted solids which may be deposited with the fibers, such as powdered asphalt or pitch, or thermoplastic or thermosetting phenol-aldehyde or other resin. Thermosetting resin may be carried by the fiber, for example, in the manner described in Heritage US. No. 2,757,150. This patent describes application of a solution of phenol-formaldehyde resin to fibers as they are discharged from formation in the Asplund machine. The resin is dried as a coat on the fibers without thermosetting it. Liquids for spraying binder onto the falling fibers or onto the face of the growing mat may be solutions, dispersions or emulsions of binder solids. Such solids may be asphalt, rubber, synthetic resinous materials, such as polyvinyl acetate, polyvinyl chloride, and other synthetic resinous latices.

In general, to effect the desired tack, the water content is minimized, requiring use of liquids with a high solids content, which are sprayable. These requirements make it difficult to use a sol of pearl starch as binder unless high temperatures are used to produce fluidity.

To illustrate the control of water content, it has been found that in the preferred use of equal parts of the materials ALS (a lignin compound) and PF (a phenolaldehyde resin), both later identified herein, in water at 30% solids, applied at parts of solids to 100 parts of Asplund fiber having about 6% moisture, the total moisture content at the time of forming the mat and compressing the same is best in the range from 7 to 14 parts per 100 parts of total dry weight content.

The preferred method of carrying out the invention is to spray liquid into the falling material as it is dispersed in air. This requires suitably fluid liquids and this imposes limits on solids content. The tackifying agent and the binder may be separately sprayed, but to assure uniformity in the combination of the two agents, they are best combined in one liquid for spraying. Water is the preferred vehicle. To combine the two agents in water, they must be chosen for compatibility. When the two agents are not compatible in water, and even when they are, each may be sprayed separately into the falling material.

The requirements of compatibility, of high solids content, and of sprayable fluidity, make it impossible to combine each tackifier with any binder. For practical purposes, the following examples illustrate the invention by use of liquids sprayed at 30 parts of solids content per parts of sprayable liquid.

In the examples to follow ALS designates a commercial dry powder containing about 60% of ammonium lignin sulfonate at a pH of about 7. It is soluble in water and at high concentration is very tacky. In water with 30% of solids it is compatible with numerous water-soluble and water-dispersible thermosetting phenol-formaldehyde resins, with polyvinyl acetate emulsions, and with watersoluble thermosetting urea-formaldehyde resins.

In selecting thermosetting resin it is preferable to select one which does not penetrate fibrous material during the process, such as one of high molecular weight, which in a solution in water gives a non-penetrating viscosity. If necessary, a supply of resin which will penetrate may be advanced by heating it. This matter of penetration is important only with vegetable material. When mineral fibers are used, the matter of penetration need not be considered, and the degree of advancement of the resin is not important.

A suitable commercial phenol-formaldehyde resin dispersion at 65% solids is available for use without need for advancement, and is herein designated PF for convenience in reference to it. PF is sold as DUREZ 14170 by Durez Plastics Division of Hooker Chemical Corp. PF is an aqueous liquid resin of 65% solids of the onestep type having a pH of 8.0 and a limited water-tolerance, and being capable of self-emulsification when the watertolerance is exceeded. It cures at 165 C. in 37 seconds and at C. in 57 seconds. At 30% combined solids, both ALS and PF are compatible in water in limited proportions for use in the following examples. They are compatible at equal parts, but not compatible when using 2 parts of ALS to one part of PF.

To illustrate variations of the invention, wood fiber from the Asplund process is dispersed in air for gravity deposition in a chamber to form a mat, and as it falls liquid at 30% solids is sprayed into the stream of fibers to introduce 15 parts of solids per 100 parts of fiber (air dry basis), either as one liquid or as separate liquids. The mat piles high because of the resulting tackiness of the depositing and deposited fibers.

The mat, While still tacky, is compressed in varying degrees. With low compression, a flexible blanket can be formed of density, for example, in the range from 2 to about 10 pounds per cu. ft. With higher compression, a mat is formed, which when bonded by setting the adhesive, is a rigid board. Rigid boards in the density range of about 10 to about 25 pounds per cu. ft. are suitable for thermal insulation and acoustical uses, and in the range from about 25 to 60 or more, are suitable for structural uses, the lower density structural boards also providing thermal insulation. Where high strength of boards is an important objective, the kinds and proportions of tackifier and of binder are chosen for this result. After compression, the resulting fiber felt is heated to thermoset the resin, for example, at a temperature in the range 300 F. to 450 F., with or without restraint.

The phenolic resins are preferred as binders when using a lignin compound, because of the greater strength and water-resistance imparted to the products. It is known that lignin compounds react with phenol-aldehyde resins, and experience with the present invention indi- Parts Per 100 of Fiber Modulus of Example Rupture,

lbs/sq. inch Tack Binder The following examples with Asplund fiber show various combinations of tack and binder each sprayed at the same time from separate nozzles, in Examples 5 to 7 in an aqueous liquid at 30% solids, and in Examples 8 and 9 the two components were combined in one liquid at 30% solids:

Parts by Weight per 100 of fiber Modulus of Example Density, Rupture,

lbs./cu. it. lbs/sq. inch Tack Binder 7.5 LigninA 7.5 P11- 29 1,340 7.5 ALS 7.5 PF 28. 3 1, 623 7.5 Vinsol n... 7.5 PF 28. 4 1, 472 7.5 ALS 3 7.5 PF.. 31. 9 2, 407 7.5 MLS 4 7.5 P 30.0 2,030

A sulfate process lignin compound sold as Indulin B by West Virginia Paper & Pulp 00. It is a water-soluble sodium salt.

igrepared as a 40% emulsion of its melted form and reduced to 30% so 1 s.

1 ALS converted to sodium salt by addition of caustic soda.

A water-soluble lignin sulfonate sold as MARASPERSE OB by Marathon Division of American Oan Company.

The following examples show use of tack means of the carbohydrate class, used at 30% solids in water with Asplund fiber. The deposited mats were compressed to boards using a press temperature of 45 0 F.

Parts by Weight per 100 of fiber Modulus of Example Density, Rupture,

lbs/cu. ft. lbs/sq. inch Tack Binder 7.5 Sucrose 7.5 PF- 29 1, 523 2.5 Starch L 29. l 1, 805 7.5 Dextrose 26. 8 1, 029 12 Dextrin Gu111 6 PF 28. 4 979 1 Hydrolized starch by enzymes.

The density of the felt may be varied as shown by the following examples with Asplund fibers.

The foregoing shows that at densities at least as high as 30 lbs./cu. ft., the combinations of tack and binder are synergistic with respect to strength and that as the felt is more dense the synergistic benefits of the invention lessen with respect to strength, because the effect of the felting is lessened by the degree of consolidation. However, the improvement in uniformity resulting from initial low density of the mat is not lost.

Particle b0ard.-Particles of wood in the forms suitable for forming particle board, are agitated in air and sprayed with liquid containing tackifier and binder. The particles are then deposited individually by gravity to form a mat. The mat is then compressed and the binder set by heat at 450 F. The following table shows the results:

Parts per of Wood Board Modulus of Ex. Density, Rupture,

lbs/cu. it. lbs./sq. inch Tack Binder No. 1A water-soluble lignin sulfonate sold as Marasperse CB by Marathon Paper Company.

N o. 2A phenol-formaldehyde aqueous solution having from 48 to 50% solids at pH 9.5 to 9.9, sold as Forasite.

No. 3An extract of Douglas Fir bark sold as Rayonier HT by Rayonier, 1110., being a lignin compound similar to Indulin B.

In using ALS its tack may be increased by inclusion of 1 part of potassium dichromate per 100 parts of ALS. Example 31.A mat (Case A) of Asplund fibers is formed by depositing the same through an aqueous spray containing 30% solids and providing 7.5 parts of corn syrup solids and 7.5 parts of polyvinyl acetate latex solids in emulsion form per 100 parts of air-dry fiber. A like mat (Case B) was made using 15 parts of corn syrup solids per 100 parts of fiber, and another (Case C), using 15 parts of the said latex solids.

The three mats were compressed to boards A, B and C of about 40 pounds per cu. ft., while heating at 450 F., with strengths as follows:

Modulus of Rupture (lbs./sq. inch) Example 32.-Resin-bearing fibers are prepared, and in suitably dry condition for air-laying, are sprayed when dispersed in air, with the tackifying agent. Among various ways to prepare such resin-bearing fibers, of which the resin content is activatable to bind the fibers is that shown in Heritage U.S. No. 2,757,150, showing also apparatus for air-laying the fibers by differential pressure.

Said patent is referred to for detail, briefly to carry out the following procedure. Wood is defibered in the Asplund defibrator at the discharge outlet of which a liquid resin solution is injected into the fibers carried in a current of steam. Phenol-formaldehyde resin, such as identified therein is precipitated on the fibers, and the resin-coated fibers are quickly dried by a system of conduits and cyclones. The resin-coated fibers are then dispersed through air from a region of superatmospheric pressure to a screen over a suction box to air-lay a mat.

According to a related Heritage patent, US. No. 2,757,149, it is possible to apply from small to large amounts of resin to the fiber, one example indicating 7.8 parts per 100 parts of Asplund fiber, which is substantially the same as preferred in the foregoing examples.

While the resin-coated fibers are being air-laid, by any of the methods referred to, the tackifying agent is sprayed into them. By providing resin dried onto the fibers, questions of compatibility with tack means in one liquid form are avoided.

Preferably, an aqueous liquid of a lignin compound, as described above, is preferred, such as a water-solution 7 of ALS at 30 parts per 100 parts of solution. With 7.5 parts of phenol-formaldehyde resin to 100 parts of fiber, and application of 7.5 parts of ALS, it is assured that the lignin will enter the resin bond, when curing the resin, to yield a water-resistant board from which lignin and resin may not be extracted.

Examples 33 and 34.A mixture 95 parts of slag wool and parts of sulfite cellulose fibers is deposited in a gravity chamber and sprayed with liquid at 30% solids as indicated below to introduce parts of solids per 100 parts of fiber. The mat is pressed at 450 F. to felt it to a density in the range of 12 to 14 pounds per cu. ft.

It is, of course, to be understood that properties of the product, such as water-resistance, are greatly influenced by the choices of the tack and binder. Use of watersoluble tack means does not mean that it remains in the product. It has been determined that the water-soluble lignin sulfonate salt is not extractable from the product when phenol-formaldehyde resin is used as binder. It becomes involved in the curing reaction of the resin, and obviously, participates as tack in forming the mat, and participates as a component of the binder in the final product. Accordingly, it does not follow that when water-soluble tack-producing means is employed, such means need remain water-soluble in the product.

The process is illustrated in the accompanying drawing in which the particles are represented by feltable fibers.

The drawing shows how the invention may be carried out by use of the method and apparatus to produce a mat substantially free from two sidedness.

Numerals 10 and 12 represent duplicate reversely positioned gravity deposition chambers separated by a space 14, in which is an operators platform 16. A continuous conveyer belt 18 runs from roll 20 through both chambers 10 and 12 and space 14 to return roll 22, located beyond the discharge end 24 of chamber 12. Between said end 24 and return roll 22 is located compressing means for the mat 26 discharged from chamber 12. Said means comprises at least one roll pressing onto the mat over a supporting roll below belt 18. Two such supporting rolls 28 and 30 are shown and two compressing rolls 32 and 34. Thus, the compression may be stepwise by use of more than one roll when the extent of compression is great, as in making the more dense products.

In the chamber 10, a discharge nozzle 36 is shown for dispersing the particles to form the mat, such as wood fibers for which a fiber disperser 38 is shown, such as is described in said Patent No. 2,646,381. Two other nozzles 40 and 42 are shown located below the nozzle 36 to discharge their contents into the stream 44 of falling particles from nozzle 36. One or both of the nozzles 40 and 42 are used according to the operation selected, as described above. In chamber 10, a half-mat 46 builds up with some layered variation in particle content due to a degree of fractionation effected in the spread of the discharge 44. The three nozzles, their actions, and the disperser in chamber 10 are duplicated in chamber 12, these being particle nozzle 48, a disperser 50, the two nozzles 52 and 54. The dotted line 56 indicates diagrammatically a common supply of material for the particles discharged by nozzles 36 and 48, which particles may or may not carry binder as above stated. Numerals 58 'and 60 represent, respectively, common supplies for the discharges, respectively, of nozzles 40-52 and nozzles 42S4.

When each chamber 10 and 12 discharges like the other, the particle-stream 62 in chamber 12 likewise effects a degree of fractionation. As a result, the material deposited first in chamber 10 on the conveyer 18 has the same character as the material last deposited in forming the half-mat 64 in chamber 12, with intermeshing into the half-mat 46, thus completing for discharge said mat 26. Because of the low density of the half-mat 46 and the lack of compression of it in the cross-over space 14, it is receptive of particles from stream 62 with the result that the intermeshing or interfelting of the particles within the two half-mats and between the two halfmats is substantially the same.

By the compression with one or both of rolls 32 and 34, the mat 66 is densified as desired to a mat 60, which is moist and ready for thermosetting the binder and drying. The compression may be so light as to form a lowdensity flexible mat, or higher to form a low-density moderately rigid m'at, or still higher to form a rigid board.

It is preferred to transfer the mat 66 from conveyer 18 before entering a drier 68 through which the mat passes on second conveyer 70 running between rolls 72 and 74, at the same linear speed as conveyer 18, thus discharging a dry mat 76.

The invention may be applied to a variety of materials containing feltable and intermeshable particles, and may use a variety of combinations of tack means and binder, other than those specifically disclosed to illustrate the invention as expressed in the appended claims.

We claim:

1. In the process of mechanically converting a supply of material into intermeshable particles dispersed in air, and depositing the particles and activatable binder from air suspension in superimposed random relation to form a mat, the steps of applying to the particles while suspended in air means to provide tack, whereby said tack, whereby said tack on deposition of the particles creates resistance to inte-rmeshing with the previously deposited particles, shifting positions of deposited particles to effect a predetermined form, and activating the binder to fix the positions of particles in said form.

2. The process of claim 1 in which the particles predominate in feltable fibers.

3. In the process of mechanically converting a supply of material into intermeshable particles dispersed in air, and depositing the particles and activatable binder from air suspension in superimposed random relation to form a mat, the steps of applying to the particles while suspended in air means to provide tack, whereby said tack on deposition of the particles creates resistance to intermeshing with the previously deposited particles, compressing t-he deposited mat toward uniform thickness whereby during compression deposited particles thereof may move laterally in the mat, and activating the binder in the compressed mat.

4. In the process of mechanically converting a supply of material into intermeshable particles dispersed in air, and depositing the particles and binder from air suspension in superimposed random relation to form a mat, the steps of applying to the particles while suspended in air, first means to provide tack and aqueous liquid containing second means to provide said binder, whereby said tack on deposition of the particles creates resistance to intermeshing with the previously deposited particles, compressing the deposited mat toward uniform thickness whereby during compressing deposited particles thereof may move laterally in the mat, and heating and drying the compressed mat under conditions to set the binder.

5. In the process of mechanically converting a supply of material into intermeshable particles dispersed in air, and depositing the particles and binder from air suspension in superimposed random relation to form a mat, the steps of applying to the particles while suspended in air first means comprising an aqueous liquid containing a lignin derivative capable of providing tack on the surface of suspended particles and second means comprising an aqueous liquid containing binder for the particles, the total amount of Water present including the moisture content of the particles before application of said liquids being such as to effect formation of a mat by deposition of tacky-surfaced particles, compressing the deposited mat toward uniform thickness whereby during compression deposited particles thereof may move laterally in the mat, and heating and drying the compressed mat under conditions to set the binder.

6. In the process of mechanically converting a supply of material into intermeshable particles dispersed in air, which particles predominate in felt'able fibers, and depositing the particles and binder from air suspension in superimposed random relation to form a felt, the steps of applying to the particles while suspended in air first means comprising "an aqueous liquid containing a lignin derivative capable of providing tack on the surface of suspended particles and second means comprising an aqueous liquid containing binder for the particles, the total amount of water present including the moisture content of the particles before application of said liquids being such as to effect formation of a felt by deposition of tacky-surfaced particles, whereby said tack on deposition of the particles creates resistance to intermeshing 'with the previously deposited particles, compressing the deposited mat toward uniform thickness whereby during compression deposited particles thereof may move laterally in the mat, and heating and drying the compressed mat under conditions to set the binder.

7. The process of claim 6 wherein the lignin derivative is a water-soluble salt of lignin sulfonic acid, and wherein the binder is activatable phenol-formaldehyde resin.

References Cited by the Examiner UNITED STATES PATENTS 2,569,169 9/1951 Heritage 264-121 X 2,604,427 7/1952 Armstrong et a1 156-26 2,664,377 12/1953 Van Beckum et al. 156-336 2,757,115 7/1956 Heritage 264121 X 2,849,314 8/1958 Goss 260124.3 2,934,531 4/1960 Gardon et a1. 260124 3,085,926 4/1963 Snyder 260124 X EARL M. BERGERT, Examiner.

J. F MATHEWS, Assistant Examiner. 

1. IN THE PROCESS FO MECHANICALLY CONVERTING A SUPPLY OF MATERIAL INTO INTERMESHABLE PARTICLES DISPERSED IN AIR, AND DEPOSITING THE PARTICLES AND ACTIVATABLE BINDER FROM AIR SUSPENSION IN SUPERIMPOSED RANDOM RELATION TO FORM A MAT, THE STEPS OF APPLYING TO THE PARTICLES WHILE SUSPENDED IN AIR MEANS TO PROVIDE TACK, WHEREBY SAID TACK, WHEREBY SAID TACK ON DEPOSITION OF THE PARTICLES CREATES RESISTANCE TO INTERMESHING WITH THE PREVIOUSLY DEPOSITED PARTICLES, SHIFTING POSITIONS OF DEPOSITED PARTICLES TO EFFECT A PREDETERMINED FORM, AND ACTIVATING THE BINDER TO FIX THE POSITIONS OF PARTICLES IN SAID FORM. 